I use this lens primarily on the R5. It is worth US$900, (got it when it went on sale) I have captured many great images with this lens. Since it is such a long focal length, which means the field of view is quite small. And that means it is difficult to find the bird in the viewfinder. It is even more difficult to find a bird in flight. With many practices, it makes it a little easier but it is still quite a challenge since you only have a couple of seconds to find the bird in flight and focus and shoot. What helps is that the lens is light, so it is not tiring when shooting handheld for an hour or so.
I gave it 5 stars, because it is delivers sharp picture and it is inexpensive for that focal length.
No editing on the deer pic.
Value for money can't be criticised, it's an outstanding lens for the money so for anyone looking for reach on a more limited budget I would thoroughly recommend buying one.
I like the design, the way you extend it for use then reduce it's size for storage or carrying around. Having said that carrying it isn't as convenient as it might be as there is no lens tripod foot to use as a carry handle.
You are limited to around 25% of the viewfinder for AF points and it seems to have more difficulty in using eye detect than other lenses I have.
The IQ is good, not quite as good as the 100-500 as you'd expect but compare the price!
I'd forget the idea of using a TC with it though despite the fact that it's currently one of only a few RF lenses that is compatible.
I got this lens to extend my reach for bird photography beyond my EF 100-400 MII. It does a very good job in adequate light. It is easy to hand hold for hours, comparable to the EF 100-400. It is compact and compresses to fit into my standard camera bag, IS works well. Focus is fast and eye focus works well in good light.
This lens is fixed aperture f/11 and requires adequate light for best performance. It does take advantage of the high ISO capability of the R5. I utilize auto ISO and TV mode often with this lens. There are still limitations with subjects in deep shade. I live in SE Arizona. Low light is rarely an issue for me.
The minimum focus distance of 6 meters was a limiting factor for me while shooting from a blind. Perhaps I am spoiled by the close MFD of the EF 100-400 MII.
Overall, this is an excellent hand held lens for the R5 and is reasonably priced.